High water solubility is a key feature of prior art glass fiber bonding resins used in the preparation of resinated glass wool. High water solubility is normally provided by formulating these resins (e.g., phenol/formaldehyde-resole resins or melamine/formaldehyde resins) with high formaldehyde to phenol molar ratios or with high formaldehyde to melamine molar ratios (near or above 3:1 in either case). Reaction products are respectively monomeric methylol phenols and methylol melamines. The methylol melamines are normally stabilized by further reaction with methanol to form the water soluble methoxy methyl melamine derivatives.
A high content of unreacted formaldehyde is therefore often found in prior art resins of these types as a consequence of the high formaldehyde ratios employed to prepare them.
Application of heat to thermally set (polymerize) these types of conventional resole resins in curing operations also causes the release of additional amounts of formaldehyde from condensing methylol groups in the resole resins and from condensing methoxy methyl groups in the melamine resins.
The release of irritating formaldehyde gas from resin impregnated, also called resinated, glass wool or glass fabrics during molding and shaping operations may be objectionable both from an environmental, and industrial hygienic point of view.
Formaldehyde release during curing of the resin is also a problem with the well-documented use of mixtures of these two types of resins. It has therefore been necessary and common industrial practice to control formaldehyde evolution into the environment and work place during curing and B-staging operations, by compounding these methylol phenol and methoxy methyl melamine binders, or mixtures of the two, with significant amounts of urea and/or ammonia. Urea and ammonia have very high reactivities towards free or uncombined formaldehyde and readily affect its capture from aqueous A-stage solution compositions. The products from such scavenging reactions are dissolved methylol urea monomers and hexamine (also called hexamethylenetetramine), respectively. Mixtures containing methylol ureas may still be problematic, however, as the thermally-induced condensation reaction between methylol ureas also releases formaldehyde.
Additionally the use of urea and particularly ammonia as formaldehyde scavengers results in the formation and release of undesirable trimethyl amine through various, thermally-induced decomposition reactions. The formation of trimethyl amine from ammonia and formaldehyde is a well-documented reaction. Trimethyl amine, although possibly not as volatile or irritating as formaldehyde, does have an objectionable, foul smelling "fishy" odor. Trimethyl amine also has a low human threshold odor limit in the low parts per billion range.
The trimethylamine problem is particularly pronounced in high density molded articles prepared with high binder contents as the curing operation traps evolved gasses inside the mold, and subsequently inside the glass fiber resin matrix, which gives the finished article a long-lasting unpleasant trimethylamine odor. Less dense articles, such as residential thermal insulation that are cured by blowing heated air through the resinated glass wool blanket, may have less odor in the finished article. The escaping trimethylamine gas purged from the curing blanket by the hot air flow nonetheless ends up in the environment. The use of urea and/or ammonia to scavenge or capture formaldehyde in these binders therefore may not satisfy environmental restrictions on fiberglass plants and the increasing quality (odor free) standards for finished products.
These decomposition reactions occur as a result of the inherent thermal instability of urea and its reaction products with formaldehyde and the very high curing temperatures employed; (often above 500.degree. F.) to mold or permanently shape resinated glass wool.
Another objectionable problem with binders and resinated wool containing urea is their propensity to burn, blacken and smoke during 500.degree. F. molding operations. Urea has, in fact, been added to prior art binders as an antipunk agent to reduce thermal oxidative degradation.
A need therefore exists in the art for phenolic binder compositions that cure above 500.degree. F. without the liberation of offensive odors, smoke or other volatile organic pollutants.
The art has previously recognized the outstanding high temperature and antipunk properties of binders prepared from melamine added to a phenolic resole. All known prior art binders, however, which specify compositions containing melamine use either a high formaldehyde containing-resole where a methylol melamine derivative is formed, or the melamine has been added to the phenol as a methoxy methyl melamine derivative. These approaches have provided dissolved melamine resin solutions or water soluble melamine-containing binders. The prior art often uses the term "melamine" to include both melamine per se and also derivatized melamine, such as methylol melamine. Thus, herein the term "melamine crystal" means melamine, per se, and underivatized in powder, crystalline, or flake form. This shall include, for example, and not by way of limitation, MCI's GP (General Purpose), non-recrystallized grade of melamine powder. Melamine crystal herein shall also mean 1,3,5-triazine-2,4,6-triamine; 2,4,6-triamino-S-triazine; and cyanurotriamide.
U.S. Pat. No. 4,960,826, issued Oct. 2, 1990 to Walisser, teaches binder compositions comprising resole resins copolymerized with melamine. The materials of U.S. Pat. No. 4,960,826 are prepared by mixing the alkaline high formaldehyde containing resole and melamine preferably at elevated temperatures and resulted in dissolving all of the melamine in the resin (column 11, line 4). This produced a clear very high solids resin solution as a one-piece binder system, which however suffered from pre-cure, or advancing of the resin during application. A dispersion was not taught in U.S. Pat. No. 4,960,826.
U.S. Pat. No. 4,757,108, issued Jul. 12, 1988 to Walisser, teaches binder compositions comprising resole resins reacted with urea. The resulting resin solution was clear with no undissolved components, and did not utilize melamine.
The teachings of Deuzeman U.S. Pat. No. Re. 30,375 fundamentally advance the concept of a high formaldehyde ratio to achieve high phenol conversions. This results, however, in finished products with, for the purpose of the current invention, undesirably high levels of free or uncombined formaldehyde.
U.S. Pat. No. 4,785,073, issued Nov. 15, 1988 to Farkas, et al., teaches melamine-phenol-formaldehyde resole modified compositions. The compositions of Farkas, et al., however, are produced using mildly alkaline conditions at pH 7.2 to 8.5, unlike the strongly alkaline compositions of the present invention. Furthermore, Farkas, et al. requires the presence of a glycol or glycol derivative unlike the present invention.